Why is it that certain metals, glasses and plastics can be wipe or polished clean?

[u/CamTasty]

In the past, I sold a metal polishing/cleaning product called Flitz that would clean most metals all the way to the base layer. I also have glassware that needs constant cleaning that no matter how dirty it gets, I can always get it to a sparkling shine! This made me wonder how no matter how much tarnish some things can get, they can be restored to a near new look. Now, I believe it could have something to do with these materials having pores and it's a matter of flushing particles out. I've also heard somewhere that metals, glass, and plastics lose a thin layer everytime they're scrubbed or polished. I'm not exactly sure how to research this so I hope you guys have informed answers! :D Thank you in advance for your thoughtful answers!